Add server-wide and user-only federation controls (#133)

### Description

Completes #122

### Please confirm

- [x] I am the legal owner or represent the legal owner of all work submitted (including LLM-generated code, if any)
- [x] I consent to my changes being added to this FOSS project
- [x] I have confirmed that this does not add new errors or warnings with `utils/clippy.sh`
- [ ] This PR used LLMs to generate some or all of the code changes

Reviewed-on: https://git.ngram.ca/OpenJam/rc-servers/pulls/133

assets/templates/rc_society/login.html.hbs

@@ -98,6 +98,9 @@
       background-color: lightgrey;
       font-size: 20px;
     }
+    input[type=submit] {
+      cursor: pointer;
+    }
     .input-required-hint::after {
       color: red;
       /*content: "*required";*/